userfaultfd: don't BUG_ON() if khugepaged yanks our page table
authorJann Horn <jannh@google.com>
Tue, 13 Aug 2024 20:25:22 +0000 (22:25 +0200)
committerAndrew Morton <akpm@linux-foundation.org>
Mon, 2 Sep 2024 00:59:00 +0000 (17:59 -0700)
commit4828d207dc5161dc7ddf9a4f6dcfd80c7dd7d20a
tree8dc1897967f79d74885f6abd07af6de02c538d60
parent71c186efc1b2cf1aeabfeff3b9bd5ac4c5ac14d8
userfaultfd: don't BUG_ON() if khugepaged yanks our page table

Since khugepaged was changed to allow retracting page tables in file
mappings without holding the mmap lock, these BUG_ON()s are wrong - get
rid of them.

We could also remove the preceding "if (unlikely(...))" block, but then we
could reach pte_offset_map_lock() with transhuge pages not just for file
mappings but also for anonymous mappings - which would probably be fine
but I think is not necessarily expected.

Link: https://lkml.kernel.org/r/20240813-uffd-thp-flip-fix-v2-2-5efa61078a41@google.com
Fixes: 1d65b771bc08 ("mm/khugepaged: retract_page_tables() without mmap or vma lock")
Signed-off-by: Jann Horn <jannh@google.com>
Reviewed-by: Qi Zheng <zhengqi.arch@bytedance.com>
Acked-by: David Hildenbrand <david@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Pavel Emelyanov <xemul@virtuozzo.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
mm/userfaultfd.c